Magnetic material



Patented Dec. 16, 1930 UNITED STATES PATENT OFFICE WIEBOLD FRANSBRANDSMA, POPKO REINDER DIJ'KSTERI-IUIS, GERARDUS JOHANNES SIZOO, ANDGOTTFRIED BRUNO JONAS, 01? EINDHOVEN, NETHERLANDS, ASSIGNORS TO RADIOCORPORATION OF AMERICA, A CORPORATION OF DELAWARE MAGNETIC MATERIALApplication filed August 1, 1928, Serial No. 296,665, and in theNetherlands July 19, 1927.

This invention has reference to a magnetic material. As is Well known inpractice, it is possible by special heat operations to exercise a greatinfluence on the properties of magnetic material. When, for example, thematerial has been decarbonized-byheat in air or oxygen, it will be foundon experimentation that the permeability has increased. Consequently, itis apparent from the hysteresis curve of the material thus produced thatat small values of the intensity H of the magnetic field the curveascends steeply and then passes rather sharply into the zone ofsaturation.

Let it be assumed that this material is used as the core of alow-frequency transformer and that this transformer is'connected in anamplifying stage of a receiver unit for radio-telephony. To the directcurrent corresponds a certain field intensity H and to the alternatingcurrent a cyclically varying field'intensity A H. Now, the variations inthe flux B are measured and the coefli-cient of the maximum A B and themaximum A H, i. e.

maximum A B maximum A H is determined. I

These measurements at diflerent values of H show that the coefficientmaximum A B maximum A H hereinafter referred to as efiectivepermeability, depends greatly on the various intensities of field H atwhich the cyclically varying A H occurs.

operations is that the efiective permeability dependings greatly on thevalue of the A Hand consequently on the amplitude of the alternatingcurrent. It is desirable that this phenomenon should not occur and thatthe effective permeability at different values of H should have largeand practically constant values. The invention has for its object to soworlz the material that this requirement is. met. i

According to the invention the previously Another fact that isdistinctly pronounced during the measuring contrary the effectivepermeability through-.

out the same zone is large and practically constant. The linearity ofthe curve of hysteresis also results in the effective permeabilitydepending only slightly on the value of A H and consequently on thealternating current amplitude. In addition, in contradistinctlon to thepreviously used material, this material has a small residual magnetismat a normal coercive force.

The explanation of these phenomena is due in all probability to the factthat owing to oxidation of the material microscopically small fissuresare produced which act as air gaps and consequently bring about thetypical progress of the curve of hysteresis.

The material produced by the process of the invention is pro-eminentlysuitable for use as the core of a transformer or as some part of-it,such as a lamella or a transformer sheet. Very good results have beenobtained by subjecting to the process of the invention an alloy of ironcontaining at least 40% of nickel.

If, for example, transformer-completes containing 50% nickel andapproximately 0.095% carbon are heated in air at a temperature of about900 C. during 15-20 minutes,

the material thereafter still contains approximately 0.04% carbon. Theheating operation however, should not be continued too long as otherwisethe oxidation becomes too strong and the magnetic properties growweaker.

The invention will be more clearly understood by reterence to theaccompanying drawings. In these drawings:

Figure l is a comparative View of the.

curves of hysteresis which are produced on testing a material which isonly decarbonized, and a material which is worked by the process of theinvention.

Figure 2 is a comparative view of the efiective permeability atdifferent values of H of the two curves of hysteresis shown in Figure 1.

Figure 3 is an enlarged view of the progress of A B at cyclicallyvarying A H.

Figure 1 shows two curves of hysteresis, curve I of a material which isonly decarbonized, curve II of a material which after decarbonizationhas been oxidized. In order that the characteristic properties of thecurves should be well pronounced they will be compared at two values ofthe intensity of field H and H. By reason of alternating currents,cyclic variations A H about the two values H and H-ensue. The variationsA B then measured show, graphically plotted, the progress as partlyshown in Figure 1 and in Figure 3. To a maximum A H corresponds amaximum A B, the coefficient of both:

maximum A B maximum A H or in other words the effective permeability,corresponds to the tangent of the angle made by the longitudinal axis ofthe loop with the H-axis (Figure 3). At the various values H and H thisangle is found to be greatly different for curve I and little differentfor curve II. In Figure 3 are plotted the variations A B at a large andat a small amplitude of A H. The effective permeability is found todepend greatly in the curve I and slightly in the curve II on theamplitude of A H.

a 1 and a 2 designate the angles at various values of H. These anglesare found to I differ much more in curve I than in curve II. In Figure 2the various values of effective permeability are measured for any pointof the curve of hysteresis and are plotted as a function of H. It isconspicuous from this graphic representation how the effectivepermeability in the case of the material I-depends greatly and in thecase of material II depends slightly on the intensity of field H.

What we claim is:

A transformer core comprising magnetic material which is substantiallydecarbonized' and partly oxidized to such an extent that the hysteresiscurve is substantially straight. WIEBOLD FRANS BRANDSMA. POPKO REIN DERDIJKSTERHUIS. GERARDUS J OHANN ES SIZOO. GOTTFRIED BRUNO JONAS.

